I have a Dell XPS laptop and it came with Windows 10 Home installed. I had a Windows 10 Professional license tied to my Microsoft account. I wanted to upgrade my Home installation to a Professional installation, here’s how I did it:

UPDATE: The following steps did not work as I had hoped. It didn’t not accept my other Microsoft account’s Windows 10 Pro license. I ended up buying the Windows 10 Pro license from Play-Asia for very cheap. I still went through steps 1-5 and then I entered the new Windows 10 Pro key. And it didn’t work! I ended up calling Microsoft and activated it over the phone. And done! 🙂

Open Windows 10 Settings and go to activation

Click on Product Key and use this one VK7JG-NPHTM-C97JM-9MPGT-3V66T. (This is a generic Windows 10 Professional key, it will simply allow you to perform the upgrade)

Perform the upgrade

After restart, Windows will ask for activation

Open Windows 10 Settings and go to activation

Click on Troubleshoot

Click on “I recently changed hardware on this device” and select the license from the Microsoft account

Sign in to your Microsoft account (the one with the Windows 10 Professional license) and voila!